Siloxane putty



Patented Aug. 26, 1952 ascertasmoxsuscrorrr IEarl L.-Warrick,Pittsburgh, Pa., assignor to Dow :,C.0rningj Corporation,Midland,*lv/.lich.; a .corporation of Michigan 1 No Drawing. ApplicationSuzie 2, 1950,

Serial No. 165,870

i mam. (c1. and) This application relates to siloxane putty and caulkingcompounds.

One of the chief disadvantages of heretofore employed puttieszandcaulking compounds is the fact that these materials. gradually hardenand crack due to action of atmospheric oxygen. This is a seriousdisadvantage in many applications, particularly in the sealing of largeglass windows such as storefronts. As a. result of this hardening, thesealing compound cracks and allows the entrance of water. Consequently,it is necessary to periodically remove the glass in order to reseal thejoint. In the case of large plate glass windows, this involvesconsiderable labor costs.

Aluminum framewindows are of great utility in homes, particularly sincethe metal does not require painting. However, it-is necessary to paintthe'putties heretofore employed in order to prevent them from cracking.Hence, one of the chief advantages of the aluminum window is lost.

It is an object of this invention to provide a putty and caulkingcompound which does not harden and crack upon exposure to theatmosphere. Another object is to provide a material which willpermanently seal glass windows. Another object is to provide a sealingcompound which is useful over a wide range of temperature. Anotherobject is to eliminate the expense and inconvenience of replacingsealing compounds.

This invention relates to a sealing compound composed essentially of abenzene soluble polymeric o-rganosiloxane having a viscosity of at least100,000 cs. at 25 0., from 100 to 500 parts by weight of a heat stableinorganic filler, and from 1 to 20 parts by weight of a silica powderhaving a pore volume of at least 4 cos. per gram, and a heat of wettingby water of from 0.3 to 1 calorie per cc. of pore volume.

The polymers employed in this invention are benzene soluble polymericsiloxanes having a viscosity of at least 100,000 cs. The polymers rangein consistency all the way up to solid non-flowing materials. Suchpolymers contain principally diorganosiloxane units in which the organicradicals are alkyl and monocyclic aryl. In addition, the polymers maycontain limited amounts of siloxane units of the type Rsiow or RsSiO1 zin which R is alkyl or monocyclic aryl. It is necessary, however, thatthe polymer be in such a state that when compounded with the filler itwill give a plastic material which can be applied readily. This may beaccomplished with the non-flowing solid polymers by employing a solvent.Thus, the.polymer-should :notbexin the form of atough insoluble gum.

The polymer and filler may be mixed inlany desired manner but, goodresultsare obtained by milling. Fillers which are-operative in thisinvention are. inorganic. heat stable materialssuch as diatomaceousearthfclay, iron oxide, alumina,

titania, calcium carbonate. and zinc oxide. The amount of these fillerswhich is employed will vary with the viscosityof. the. polymer and with.the consistency desired in the finished product.

It has been found that when the above de-- scribed siloxanesand fillersare. compounded in suchamount as to; give a consistency desired for:

.acaulking compoundgthatthe resulting material a such as burningtrichlorosilane or a mixture of silicon tetrachloride and hydrogen, andcooling the silica so produced. Alternatively, such silicas may beprepared by the well known aerogel process.

The pore volume of the silicas is determined by placing a weightedsample of the filler in a vessel and determining the weight of waterrequired to fill the vessel. The operation is then repeated with mercuryand the weight of mercury determined. The volume of water in the vesselminus the volume of mercury gives the pore volume of the sample. This isthen converted to ccs. per gram based upon the weight of the sample.

The heat of wetting by water is determined by placing a weighted sampleof water in a calorimeter. A weighted sample of the silica filler,having the same temperature as the water in the calorimeter is thenadded tothe water. The temperature rise is noted and converted to theheat of wetting by the formula where Hw is the heat of wetting incalories per gram, AT is the temperature rise in the degrees C, W5 isthe weight of silica, H is the calorimeter constant, H1 is the specificheat of water, and W1 is the Weight of water. The constant 0.188 is thespecific heat of quartz. The heat of wetting in calories per gram isthen converted 3 into calories per cc. of pore volume by dividing I-Iwby the pore volume of the silica. expressed in ccs. per gram.

Sealing compounds prepared in accordance with thi invention remainpermanently soft and non-cracking over a temperature range from below 80F. to above 300 F. They are sumciently plastic that they may be readilyapplied with a putty knife or caulking gun, and yet exhibit no coldflow. As far as is known, the performance of these materials isoutstandingly superior to any heretofore known sealing compounds. 1

If desired, pigments may be included in the composition of thisinvention to impart color thereto.

The following examples are illustrative only, and should not beconsidered as limiting the invention.

Example 1 100 parts by weight ofa non-flowing benzene solubledimethylsiloxane polymer, 300 parts by Weight diatomaceous earth,and 5parts by weight of a silica powder having a pore volume of 9.77 ccs. pergram, and a heat of wetting of 0.72 calories per cc. ofpore volume werecompounded in a mill until the ingredients were thoroughly mixed. Thresulting product was soft and extrudable but exhibited no cold flow.

The material was used to caulk an aquarium, and after 4 days'standing,no leaks had appeared.

The compound was employed as a putty in unpainted aluminum windows, andafter 9 months there was no hardening or cracking of the putty. Thewindows showed no leakage during rain.

4 Example 2 100 parts by weight of a copolymer siloxane having thecomposition mol per cent dimethylsiloxane and 5 mol per centphenylmethylsiloxane, which polymer had a plasticity of 30 (asdetermined by ASTM-D-926-4'7T), was milled with 260 parts by weight ofdiatomaceous earth and 1 part by weight based on the siloxane of asilica aerogel having a heat of wetting of 0.655 calorie per cc. of porevolume, and a pore volume of 7.32 cos. per gram. The milled material hada consistency of soft putty and was employed to seal the plate glasswindows of a store. The seal so obtained was satisfactory.

That which is claimed is:

A sealing compound comprising (1) an organopolysiloxane in which theorganic radicals are selected from the group consisting of alkyl andmonocyclicaryl radicals, said siloxane being benzene soluble and havinga viscosity of at least 100,000 cs. at 25 C., (2) from 1 to 20 parts byweight based upon parts by weight of (1) of a silica powder having apore volume of at least 4 cc. per gram and a heat of wetting of from 0.3to 1 calorie per cc. of pore volume, and (3) from 100 to 500 parts byweight based upon 100 parts'by Weight of (1) of a filler other than (2).

EARL L. WARRICK.

REFERENCES CITED The following references are of record in the file ofthis patent:

